Solar light is one of our natural resources which is available free or charge and which causes no negative environmental side effects when used. Light is shown to consist of particles when measured by some methods and waves when measured by other methods. The conclusion to this phenomena is that light is somehow both a wave and a particle—or that it's something else we can't quite visualize, which appears to us as one or the other depending on how we look at it.
Light is part of the electromagnetic spectrum that includes radio, television, gamma and x-rays. Light is a very small part of the vast electromagnetic spectrum where such phenomena are found. When measured as a wave, white light, as we see it, is composed of waves with physical lengths from about 800 nanometers to 400 nanometers. A nanometer is 1×10−9 meter or 0.000000001 of a meter. Since the waves of light are in constant motion they can be considered as vibrations with an up and down movement when viewed from one perspective. When the light wave travels through one up and one down motion the movement is known as one cycle. The recurrence of these cycles during one second is known as the frequency of light. The waves of light travel at 300,000 meters per second which is known as “the speed of light” in a vacuum and thus a relationship between the frequency and the wavelength of light can be made.
The particles of light are known as “photons”. A Photon is considered the smallest unit of light energy or electromagnetic radiation. Max Planck and Albert Einstein, Nobel Prize winners in physics, discovered that light, which usually travels in waves, sometimes behaves as if it were made up of a stream of individual small quantities called quanta or particles of energy. The term “photon” was coined by Gilbert Lewis in 1926.
The photon is one of the elementary particles of nature. Its interactions with electrons and atomic nuclei account for a great many of the features of matter, such as the existence and stability of atoms, molecules, and solids. In some respects a photon acts as a particle, for instance when detected by the crystalline structure of a light sensitive device in a camera. In other respects, a photon acts like a wave, as when passing through the optics in a camera.
Photons are produced by the collision of atoms when a bound electron moves from one orbital of high energy to another orbital with less energy. Photons have zero mass and zero electric charge, but they do carry energy. The energy of a photon can be transferred when a photon interacts with an electron within a crystalline structure such as that contained within a solar cell. Thus electricity can be created from energy produced when an electron moves within an atom to produce a photon which then travels elsewhere to finally impact another electron within a crystalline structure causing the new electron, independent of the first, to move creating an electric charge.
Atoms continuously emit photons due to their collisions with each other. The wavelength distribution of these photons is thus related to their absolute temperature with the probability of a photon being a certain wavelength determined by the temperature of the creating atom. The spectrum of such photons is normally peaked in the range between microwave and infra-red, but sufficiently hot objects (such as the surface of the Sun or a light bulb filament) will emit visible light as well. Normally, light is formed from a large number of photons, with the intensity related to the number of them.
Solar energy concentration devices are those appliances that can increase the amount of light or photonic energy generated at the sun by directing large volumes of continuous light into smaller volumes of space. We call this concentration of light. Light is not amplified, just concentrated. Such appliances include devices that make use of a lens or multiple lenses to focus an area of incoming light into a fine point. A refracting solar telescope makes use of several lenses to accomplish this task. On the other hand, lens-less systems make use of reflecting surfaces to focus an area of incoming light into a single fine point. The reflectors and/or lenses used in conventional collectors to focus the light beams are subject to heat production from the infra-red component of the incoming solar light and must be cooled or otherwise controlled to prevent destruction of the various components of the system. Use of this destructive component is found as the desirable feature in solar cookers. However, where the collection of and concentration of photonic energy for the purpose of producing high intensity light is concerned, such heat production is a destructive component which must be removed. What is required is a system which will eliminate or substantially remove the infra-red heat producing light while allowing the passage of the visible light. What is further required is the ability to transport the visible light to a location where it can be utilized as an energy source. Filtering enough of the heat producing light component found within the longer light wavelengths may require multiple filtering entities. This is especially true when considering the use of light concentrations above 1000 suns. The use of a solar photon filter at the concentrator input is a solution for which this invention is addressed.
Previous art is found among many U.S. patents related to light filtration methods. One such patent is U.S. Pat. No. 4,229,066 which teaches about a filter which is reflecting at a longer wavelength region and transmitting over a wide band shorter wavelength region, a substrate having a surface, and a coating carried by the surface comprising at least one period which is reflecting at longer wavelengths and transmitting in a wide band of shorter wavelengths. Another patent, U.S. Pat. No. 4,717,227 relates to a solar ray collecting device, of the type in which a large number of lenses having about 4 cm or less in diameter are used, to focus solar rays. Such a device is made up of a heat-conductive support base plate, a large number of hexagonal recess portions, a large number of optical systems installed on each of the recess portions, a large number of heat-conductive protection bars which are set up on the upper vertex of a side wall forming the recess portion, and a protection cover for a light-receiving surface side of the supporting base plate having the function of a filter which is capable of letting visible rays pass through, a pointed end portion of the protection bar being brought into heat-conductive contact with the protection cover. The use of fiber optic bundles and filters is taught in patent U.S. Pat. No. 5,231,461 where a scanning mirror rotates about an axis to sweep successive portions of the earth's terrain past a set of detectors wherein individual ones of the detectors are provided with filters for viewing reflected radiation from the terrain. The calibration system includes a fiber-optic bundle for receiving rays of light from the sun, an output end of the bundle being configured with individual fibers arranged in a line parallel to the mirror rotational axis so as to illuminate the mirror with an input slit of light.
Further examples of previous art in light filter designs are shown in patent U.S. Pat. No. 5,378,892 where an infra-red optical system including imaging optics for transmitting and focusing infra-red light from object space onto an image plane, an infra-red light detector positioned closely proximate to the image plane, a Dewar for cryogenically cooling the detector and an angle filter for restricting the field of view of the detector to a predetermined angle. Another patent, U.S. Pat. No. 6,126,869, teaches about a solar blind optical filter assembly having a class of dye materials which maximizes transmission of target radiation while minimizing transmission of solar or actinic radiation. Also, patent U.S. Pat. No. 6,903,036 further teaches filtration methods using a glass having a composition comprising a dopant as divalent copper oxide having absorption at about 800 nm and infra-red cut capability, a silica skeleton and a vitrification-aiding network modifier oxide and so suitable for vitrification. Thus, the glass of the invention can have excellent infra-red absorption capability and, at the same time, high visible light transmittance as well as chemical endurance and process ability. Another dye induced light filter is found in patent U.S. Pat. No. 6,994,885 where an optical filter is made comprising an organic, solar blind filter dye; and a UV-transparent, non-scattering and chemically stable substrate.
Other approaches to filtering light include patent U.S. Pat. No. 7,149,377 which teaches about the combining of a high-precision Fabry-Perot etalon with a variety of conditioning filters judiciously selected to effectively block completely all radiation except for the spectral line of interest. In addition, a tuning mechanism is provided to precisely control the peak frequency of the filter's output by varying the optical length of the etalon's cavity. The patent U.S. Pat. No. 7,157,159 demonstrates an infra-red ray cut filter comprising: a transparent substrate; and a multi-layer membrane including multiple high-refractive index thin membranes of no less than 16 but no more than 32 layers, wherein: a design wavelength for the thin membrane layers is 750 nm. Beyond filters, precision light manipulation is taught in patent U.S. Pat. No. 6,064,506 where an optical multipath switch having electrically switchable photonic crystals having long miniaturized needles and acting as high-precision optical mirrors with cavities between the needles being filled with nonlinear optical materials or liquid crystals having an orientation so that light hits the optical geometry at a predetermined angle and the light is capable of being coupled in and selectively out via the mirrors. Such previous art provides methods and examples of a variety of ways in which light can be filtered and manipulated to yield expected results. However, no previous art has applied the various methods and techniques of this invention to produce a light manipulating filter for the removal of the heat producing infra-red light component before the light stream is concentrated
Unlike methods found among pre art, this invention utilizes a cold mirror system which consists of individual cold mirrors each made of a transparent form or substrate, and one of its surfaces, namely the reflecting surface, consisting of a dielectric interference coating comprised of a series of thin films. The films are of alternate low and high refractive index, compared to that of the substrate, and of optical thickness equal to one quarter of the wavelength of the light for which the longest wavelength of reflectance is required. The cold mirror will have a 90% reflectance of light composed of shorter wavelengths in the visible spectrum. Reflectance rapidly falls off as the wavelength of the light increases beyond the visible waveband. The films and the substrate are effectively transparent to infra-red radiation and hence this radiation is transmitted through them. The required reflected light beam is therefore depleted of nearly 90% of infra-red light or radiation.
Hot mirrors also consist of a transparent form or substrate, and one of its surfaces, namely the reflecting surface, sustains a dielectric interference coating consisting of a series of thin films. The films are of alternate low and high refractive index, compared to that of the substrate, and of optical thickness equal to one quarter of the wavelength of the light for which the shortest wavelength of light is required which, in the case of a hot mirror is in the infra-red region. The hot mirror will have a >80% reflectance of light in the infra-red spectrum. Reflectance rapidly falls off as the wavelength of the light decreases beyond the infra-red waveband. The films and the substrate are effectively transparent to visible light and hence visible light is transmitted through them. The required reflected light beam is therefore depleted of 80% of visible light.
Both hot and cold mirrors can be used for the removal of heat producing infra-red light radiation. The removal depends upon the geometric configuration of the mirror or set of mirrors. When using a cold mirror, non-infra-red visible light is reflected from the mirror. When using a hot mirror, non-infra-red light is transmitted through the mirror.